nl80211: Add VHT 160 MHz channel flags

nl80211: Add VHT 160 MHz channel flags

This extends the previous design that covered only the VHT 80 MHz cases
for VHT channel flags. New functions are introduced to allow 160 MHz
bandwidth cases to determine the center channel and check availability
of a 160 MHz channel.

Signed-off-by: Jouni Malinen <jouni@qca.qualcomm.com>